Sara dissolved 5 g each of crushed and large sized crystal of copper sulphate in two separate test tubes containing 10 mL water. After 5 minutes of stirring, she observed that the test tube containing crushed copper sulphate had dissolved in water while the test tube containing the large sized crystal still showed undissolved form. The reason for FASTER dissolution is that the crushed copper sulphate:
Correct answer: B. have greater surface area.
- A. are more in density.
- B. have greater surface area.
- C. are low in density
- D. have smaller surface area.
Explanation
Crushing the crystal exposes far more surface to the water, so more particles dissolve at the same time and dissolution is faster. Crushing does not change the density of copper sulphate, and a smaller surface area would slow the process.
This question appeared on the UHS MDCAT 2026 paper, which you can sit online with every answer explained.
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About Factors Affecting Rate of Reaction
Reaction rate depends on the nature and concentration of reactants, pressure for gases, temperature, surface area and catalysts. Collision theory explains these effects through collision frequency, orientation and activation energy, while questions often distinguish a catalyst's effect on reaction rate from its lack of effect on equilibrium composition.
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